Engineered enzymes

ABSTRACT

The present disclosure provides engineered RNA-guided enzymes for editing live cells.

RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 16/658,948, filed 21 Oct. 2019, which claims priority to U.S. Provisional Application No. 62/748,668, filed 22 Oct. 2018.

FIELD OF THE INVENTION

This invention relates to engineered enzymes for editing live cells.

BACKGROUND OF THE INVENTION

In the following discussion certain articles and methods will be described for background and introductory purposes. Nothing contained herein is to be construed as an “admission” of prior art. Applicant expressly reserves the right to demonstrate, where appropriate, that the methods referenced herein do not constitute prior art under the applicable statutory provisions.

The ability to make precise, targeted changes to the genome of living cells has been a long-standing goal in biomedical research and development. Recently, various nucleases have been identified that allow manipulation of gene sequence, and hence gene function. These nucleases include nucleic acid-guided nucleases. The range of target sequences that nucleic acid-guided nucleases can recognize, however, is constrained by the need for a specific protospacer adjacent motif (PAM) to be located near the desired target sequence. PAMs are short nucleotide sequences recognized by a gRNA/nuclease complex, where this complex directs editing of a target sequence in a live cell. The precise PAM sequence and length requirements for different nucleic acid-guided nucleases vary; however, PAMs typically are 2-7 base-pair sequences adjacent or in proximity to the target sequence and, depending on the nuclease, can be 5′ or 3′ to the target sequence. Engineering of nucleic acid-guided nucleases may allow for alteration of PAM preference, allow for editing optimization in different organisms and/or alter enzyme fidelity; all changes that may increase the versatility of a specific nucleic acid-guided nuclease for certain editing tasks.

There is thus a need in the art of nucleic acid-guided nuclease gene editing for improved nucleases. The engineered MAD70-series nucleases described herein satisfy this need.

SUMMARY OF THE INVENTION

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other features, details, utilities, and advantages of the claimed subject matter will be apparent from the following written Detailed Description including those aspects illustrated in the accompanying drawings and defined in the appended claims.

The present disclosure provides engineered MAD70-series nucleases with varied PAM preferences, varied editing efficiency in different organisms and/or altered RNA-guided enzyme fidelity (e.g., decreased off-target cutting).

Thus, in one embodiment there is provided an engineered MAD70-series nuclease with an altered RNA-guided enzyme fidelity relative to the MAD7 nuclease where the MAD7 nuclease has the amino acid sequence of SEQ ID No. 1. In some aspects of this embodiment, the engineered MAD70-series nuclease with the higher altered RNA-guided enzyme fidelity comprises any of SEQ ID No. 4-7.

In other embodiments there is provided an engineered MAD70-series nuclease having a PAM preference different than the MAD7 nuclease having the sequence of SEQ ID No. 1. In some aspects of this embodiment, the engineered MAD70-series nuclease having an altered PAM preference comprises any of SEQ ID Nos. 2, 3, 11, 12, 13, 14, 67 or 68. In some aspects of this embodiment, there is provided a cocktail of nuclease enzymes comprising one, two, three, four, five or all of SEQ ID Nos. 2, 3, 11, 12, 13, 14, 67 or 68, and in some aspects, there is provided a cocktail of nuclease enzymes comprising one, some or all of SEQ ID Nos. 2, 3, 11, 12, 13, 14, 67 or 68 and another nuclease with a PAM preference different from SEQ ID Nos. 2, 3, 11, 12, 13, 14, 67 or 68, and in some aspects, the other nuclease has a sequence of SEQ ID No. 4, 5, 6, 7, 69-78 or 79-86.

Additionally, there is provided is an engineered MAD70-series nuclease with lower cutting activity relative to the MAD7 nuclease having the sequence of SEQ ID No. 1. In some aspects of this embodiment, the engineered MAD70-series nuclease having lowered cutting activity comprises any of SEQ ID Nos. 8-10 or 15.

Also there is provided an engineered MAD70-series nuclease with enhanced editing efficiency in yeast comprising any of SEQ ID Nos. 69-78 and 79-86.

These aspects and other features and advantages of the invention are described below in more detail.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a heatmap for certain of the MAD70-series nucleases with different PAM recognition sites. FIG. 1B is a heatmap for certain of the MAD70-series nucleases with varied fidelity as compared with the MAD7 (SEQ ID No.1).

FIGS. 2A and 2B show the results of 108 engineered MAD70-series nucleases selected from screening 1104 single amino acid variants. FIG. 2A is the plot (sum of PAM depletion vs. pos9_score) for the MAD7 nuclease having the sequence SEQ ID NO. 1, and FIG. 2B is the plot for the screened 1104 single amino acid variants.

FIG. 3 is an exemplary workflow for creating and screening engineered MAD70-series enzymes.

FIG. 4 shows the sequence of two different gRNA constructs used for depletion studies (SEQ ID No. 21-24).

FIG. 5 is a heatmap for PAM preferences for MAD70-series variants from a combinatorial library screen.

FIG. 6A is a complete NNNN PAM preference for wild-type MAD 7 (SEQ ID No. 1). FIG. 6B is a complete NNNN PAM preference for the K535R/N539S mutant (SEQ ID No. 67). FIG. 6C is a complete NNNN PAM preference for the K535R/N539S/K594L/E730Q mutant (SEQ ID No. 68).

FIG. 7 shows colonies containing editing cassettes and wild-type MAD7, MAD70-series variants K535R/N539S (SEQ ID No. 67) and K535R/N539S/K594L/E730Q (SEQ ID No. 68) mutants in relation to the wild-type MAD7 amino acid sequence.

FIG. 8 is a map of the plasmid used for the screening of nuclease proteins for genome editing activity in S. cerevisiae.

FIG. 9 shows the relative rates of genome editing at different positions of the Can1 protein locus with the indicated PAM by wild-type MAD7, and the K535R (SEQ ID No. 13), N539A and K535R/N539S (SEQ ID No. 67) MAD70-series mutants.

FIG. 10 shows the results of screening 2304 MAD70-series variants for genome editing activity in S. cerevisiae.

FIG. 11 shows quadruplicate re-testing of MAD70-series variants that demonstrated enhanced genome editing activity in S. cerevisiae.

FIG. 12 shows the results of screening 2304 MAD70-series combinatorial protein variants for genome editing activity in S. cerevisiae.

FIG. 13 shows the results of secondary screening of the MAD70-series combinatorial variant hits showing fractional difference in genome editing activity in S. cerevisiae and the multiple-comparison-adjusted P value for each variant as compared to the wild-type MAD 7 (SEQ ID No. 1) controls.

FIG. 14 shows the results of genome editing in mammalian HEK293T cells with wild-type MAD7 (SEQ ID No. 1) and MAD70-series variants with AsCas12a as a control.

DETAILED DESCRIPTION

The description set forth below in connection with the appended drawings is intended to be a description of various, illustrative embodiments of the disclosed subject matter. Specific features and functionalities are described in connection with each illustrative embodiment; however, it will be apparent to those skilled in the art that the disclosed embodiments may be practiced without each of those specific features and functionalities. Moreover, all of the functionalities described in connection with one embodiment are intended to be applicable to the additional embodiments described herein except where expressly stated or where the feature or function is incompatible with the additional embodiments. For example, where a given feature or function is expressly described in connection with one embodiment but not expressly mentioned in connection with an alternative embodiment, it should be understood that the feature or function may be deployed, utilized, or implemented in connection with the alternative embodiment unless the feature or function is incompatible with the alternative embodiment.

The practice of the techniques described herein may employ, unless otherwise indicated, conventional techniques and descriptions of organic chemistry, polymer technology, molecular biology (including recombinant techniques), cell biology, biochemistry, biological emulsion generation, and sequencing technology, which are within the skill of those who practice in the art. Such conventional techniques include polymer array synthesis, hybridization and ligation of polynucleotides, and detection of hybridization using a label. Specific illustrations of suitable techniques can be had by reference to the examples herein. However, other equivalent conventional procedures can, of course, also be used. Such conventional techniques and descriptions can be found in standard laboratory manuals such as Green, et al., Eds. (1999), Genome Analysis: A Laboratory Manual Series (Vols. I-IV); Weiner, Gabriel, Stephens, Eds. (2007), Genetic Variation: A Laboratory Manual; Dieffenbach, Dveksler, Eds. (2003), PCR Primer: A Laboratory Manual; Bowtell and Sambrook (2003), DNA Microarrays: A Molecular Cloning Manual; Mount (2004), Bioinformatics: Sequence and Genome Analysis; Sambrook and Russell (2006), Condensed Protocols from Molecular Cloning: A Laboratory Manual; and Sambrook and Russell (2002), Molecular Cloning: A Laboratory Manual (all from Cold Spring Harbor Laboratory Press); Stryer, L. (1995) Biochemistry (4th Ed.) W.H. Freeman, New York N.Y.; Gait, “Oligonucleotide Synthesis: A Practical Approach” 1984, IRL Press, London; Nelson and Cox (2000), Lehninger, Principles of Biochemistry 3^(rd) Ed., W. H. Freeman Pub., New York, N.Y.; Berg et al. (2002) Biochemistry, 5^(th) Ed., W.H. Freeman Pub., New York, N.Y.; Cell and Tissue Culture: Laboratory Procedures in Biotechnology (Doyle & Griffiths, eds., John Wiley & Sons 1998); Mammalian Chromosome Engineering—Methods and Protocols (G. Hadlaczky, ed., Humana Press 2011); Essential Stem Cell Methods, (Lanza and Klimanskaya, eds., Academic Press 2011), all of which are herein incorporated in their entirety by reference for all purposes. Nuclease-specific techniques can be found in, e.g., Genome Editing and Engineering From TALENs and CRISPRs to Molecular Surgery, Appasani and Church, 2018; and CRISPR: Methods and Protocols, Lindgren and Charpentier, 2015; both of which are herein incorporated in their entirety by reference for all purposes. Basic methods for enzyme engineering may be found in, Enzyme Engineering Methods and Protocols, Samuelson, ed., 2013; Protein Engineering, Kaumaya, ed., (2012); and Kaur and Sharma, “Directed Evolution: An Approach to Engineer Enzymes”, Crit. Rev. Biotechnology, 26:165-69 (2006).

Note that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “an oligonucleotide” refers to one or more oligonucleotides, and reference to “an automated system” includes reference to equivalent steps and methods for use with the system known to those skilled in the art, and so forth. Additionally, it is to be understood that terms such as “left,” “right,” “top,” “bottom,” “front,” “rear,” “side,” “height,” “length,” “width,” “upper,” “lower,” “interior,” “exterior,” “inner,” “outer” that may be used herein merely describe points of reference and do not necessarily limit embodiments of the present disclosure to any particular orientation or configuration. Furthermore, terms such as “first,” “second,” “third,” etc., merely identify one of a number of portions, components, steps, operations, functions, and/or points of reference as disclosed herein, and likewise do not necessarily limit embodiments of the present disclosure to any particular configuration or orientation.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications mentioned herein are incorporated by reference for the purpose of describing and disclosing devices, methods and cell populations that may be used in connection with the presently described invention.

Where a range of values is provided, it is understood that each intervening value, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges, and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either both of those included limits are also included in the invention.

In the following description, numerous specific details are set forth to provide a more thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the present invention may be practiced without one or more of these specific details. In other instances, well-known features and procedures well known to those skilled in the art have not been described in order to avoid obscuring the invention.

The term “complementary” as used herein refers to Watson-Crick base pairing between nucleotides and specifically refers to nucleotides hydrogen bonded to one another with thymine or uracil residues linked to adenine residues by two hydrogen bonds and cytosine and guanine residues linked by three hydrogen bonds. In general, a nucleic acid includes a nucleotide sequence described as having a “percent complementarity” or “percent homology” to a specified second nucleotide sequence. For example, a nucleotide sequence may have 80%, 90%, or 100% complementarity to a specified second nucleotide sequence, indicating that 8 of 10, 9 of 10 or 10 of 10 nucleotides of a sequence are complementary to the specified second nucleotide sequence. For instance, the nucleotide sequence 3′-TCGA-5′ is 100% complementary to the nucleotide sequence 5′-AGCT-3′; and the nucleotide sequence 3′-TCGA-5′ is 100% complementary to a region of the nucleotide sequence 5′-TTAGCTGG-3′.

The term DNA “control sequences” refers collectively to promoter sequences, polyadenylation signals, transcription termination sequences, upstream regulatory domains, origins of replication, internal ribosome entry sites, nuclear localization sequences, enhancers, and the like, which collectively provide for the replication, transcription and translation of a coding sequence in a recipient cell. Not all of these types of control sequences need to be present so long as a selected coding sequence is capable of being replicated, transcribed and—for some components—translated in an appropriate host cell.

As used herein the term “donor DNA” or “donor nucleic acid” refers to nucleic acid that is designed to introduce a DNA sequence modification (insertion, deletion, substitution) into a locus by homologous recombination using nucleic acid-guided nucleases. For homology-directed repair, the donor DNA must have sufficient homology to the regions flanking the “cut site” or site to be edited in the genomic target sequence. The length of the homology arm(s) will depend on, e.g., the type and size of the modification being made. In many instances and preferably, the donor DNA will have two regions of sequence homology (e.g., two homology arms) to the genomic target locus. Preferably, an “insert” region or “DNA sequence modification” region—the nucleic acid modification that one desires to be introduced into a genome target locus in a cell-will be located between two regions of homology. The DNA sequence modification may change one or more bases of the target genomic DNA sequence at one specific site or multiple specific sites. A change may include changing 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, 150, 200, 300, 400, or 500 or more base pairs of the target sequence. A deletion or insertion may be a deletion or insertion of 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 40, 50, 75, 100, 150, 200, 300, 400, or 500 or more base pairs of the target sequence.

The terms “guide nucleic acid” or “guide RNA” or “gRNA” refer to a polynucleotide comprising 1) a guide sequence capable of hybridizing to a genomic target locus, and 2) a scaffold sequence capable of interacting or complexing with a nucleic acid-guided nuclease.

“Homology” or “identity” or “similarity” refers to sequence similarity between two peptides or, more often in the context of the present disclosure, between two nucleic acid molecules. The term “homologous region” or “homology arm” refers to a region on the donor DNA with a certain degree of homology with the target genomic DNA sequence. Homology can be determined by comparing a position in each sequence which may be aligned for purposes of comparison. When a position in the compared sequence is occupied by the same base or amino acid, then the molecules are homologous at that position. A degree of homology between sequences is a function of the number of matching or homologous positions shared by the sequences.

“Operably linked” refers to an arrangement of elements where the components so described are configured so as to perform their usual function. Thus, control sequences operably linked to a coding sequence are capable of effecting the transcription, and in some cases, the translation, of a coding sequence. The control sequences need not be contiguous with the coding sequence so long as they function to direct the expression of the coding sequence. Thus, for example, intervening untranslated yet transcribed sequences can be present between a promoter sequence and the coding sequence and the promoter sequence can still be considered “operably linked” to the coding sequence. In fact, such sequences need not reside on the same contiguous DNA molecule (i.e. chromosome) and may still have interactions resulting in altered regulation.

A “promoter” or “promoter sequence” is a DNA regulatory region capable of binding RNA polymerase and initiating transcription of a polynucleotide or polypeptide coding sequence such as messenger RNA, ribosomal RNA, small nuclear or nucleolar RNA, guide RNA, or any kind of RNA transcribed by any class of any RNA polymerase I, II or III. Promoters may be constitutive or inducible and, in some embodiments—particularly many embodiments in which selection is employed—the transcription of at least one component of the nucleic acid-guided nuclease editing system is under the control of an inducible promoter.

As used herein the term “selectable marker” refers to a gene introduced into a cell, which confers a trait suitable for artificial selection. General use selectable markers are well-known to those of ordinary skill in the art. Drug selectable markers such as ampicillin/carbenicillin, kanamycin, chloramphenicol, erythromycin, tetracycline, gentamicin, bleomycin, streptomycin, rhamnose, puromycin, hygromycin, blasticidin, and G418 may be employed. In other embodiments, selectable markers include, but are not limited to human nerve growth factor receptor (detected with a MAb, such as described in U.S. Pat. No. 6,365,373); truncated human growth factor receptor (detected with MAb); mutant human dihydrofolate reductase (DHFR; fluorescent MTX substrate available); secreted alkaline phosphatase (SEAP; fluorescent substrate available); human thymidylate synthase (TS; confers resistance to anti-cancer agent fluorodeoxyuridine); human glutathione S-transferase alpha (GSTA1; conjugates glutathione to the stem cell selective alkylator busulfan; chemoprotective selectable marker in CD34+cells); CD24 cell surface antigen in hematopoietic stem cells; human CAD gene to confer resistance to N-phosphonacetyl-L-aspartate (PALA); human multi-drug resistance-1 (MDR-1; P-glycoprotein surface protein selectable by increased drug resistance or enriched by FACS); human CD25 (IL-2a; detectable by Mab-FITC); Methylguanine-DNA methyltransferase (MGMT; selectable by carmustine); and Cytidine deaminase (CD; selectable by Ara-C). “Selective medium” as used herein refers to cell growth medium to which has been added a chemical compound or biological moiety that selects for or against selectable markers.

The terms “target genomic DNA sequence”, “target sequence”, or “genomic target locus” refer to any locus in vitro or in vivo, or in a nucleic acid (e.g., genome) of a cell or population of cells, in which a change of at least one nucleotide is desired using a nucleic acid-guided nuclease editing system. The target sequence can be a genomic locus or extrachromosomal locus.

A “vector” is any of a variety of nucleic acids that comprise a desired sequence or sequences to be delivered to and/or expressed in a cell. Vectors are typically composed of DNA, although RNA vectors are also available. Vectors include, but are not limited to, plasmids, fosmids, phagemids, virus genomes, synthetic chromosomes, and the like. As used herein, the phrase “engine vector” comprises a coding sequence for a nuclease to be used in the nucleic acid-guided nuclease systems and methods of the present disclosure. The engine vector may also comprise, in a bacterial system, the λ Red recombineering system or an equivalent thereto. Engine vectors also typically comprise a selectable marker. As used herein the phrase “editing vector” comprises a donor nucleic acid, optionally including an alteration to the target sequence that prevents nuclease binding at a PAM or spacer in the target sequence after editing has taken place, and a coding sequence for a gRNA. The editing vector may also comprise a selectable marker and/or a barcode. In some embodiments, the engine vector and editing vector may be combined; that is, the contents of the engine vector may be found on the editing vector. Further, the engine and editing vectors comprise control sequences operably linked to, e.g., the nuclease coding sequence, recombineering system coding sequences (if present), donor nucleic acid, guide nucleic acid, and selectable marker(s).

Editing in Nucleic Acid-Guided Nuclease Genome Systems Generally

The present disclosure provides engineered gene editing MAD70-series nucleases with varied PAM preferences, optimized editing efficiency in different organisms, and/or an altered RNA-guided enzyme fidelity. The engineered MAD70-series nucleases may be used to edit all cell types including, archaeal, prokaryotic, and eukaryotic (e.g., yeast, fungal, plant and animal) cells although certain MAD70-series variants exhibit enhanced efficiency in, e.g., yeast or mammalian cells.

The engineered MAD70-series nuclease variants described herein improve RNA-guided enzyme editing systems in which nucleic acid-guided nucleases (e.g., RNA-guided nucleases) are used to edit specific target regions in an organism's genome. A nucleic acid-guided nuclease complexed with an appropriate synthetic guide nucleic acid in a cell can cut the genome of the cell at a desired location. The guide nucleic acid helps the nucleic acid-guided nuclease recognize and cut the DNA at a specific target sequence. By manipulating the nucleotide sequence of the guide nucleic acid, the nucleic acid-guided nuclease may be programmed to target any DNA sequence for cleavage as long as an appropriate protospacer adjacent motif (PAM) is nearby.

The engineered MAD70-series nucleases may be delivered to cells to be edited as a polypeptide; alternatively, a polynucleotide sequence encoding the engineered MAD70-series nuclease(s) is transformed or transfected into the cells to be edited. The polynucleotide sequence encoding the engineered MAD70-series nuclease may be codon optimized for expression in particular cells, such as archaeal, prokaryotic or eukaryotic cells. Eukaryotic cells can be yeast, fungi, algae, plant, animal, or human cells. Eukaryotic cells may be those of or derived from a particular organism, such as a mammal, including but not limited to human, mouse, rat, rabbit, dog, or non-human mammals including non-human primates. The choice of the engineered MAD70-series nuclease to be employed depends on many factors, such as what type of edit is to be made in the target sequence and whether an appropriate PAM is located close to the desired target sequence. The engineered MAD70-series nuclease may be encoded by a DNA sequence on a vector (e.g., the engine vector) and be under the control of a constitutive or inducible promoter. In some embodiments, the sequence encoding the nuclease is under the control of an inducible promoter, and the inducible promoter may be separate from but the same as an inducible promoter controlling transcription of the guide nucleic acid; that is, a separate inducible promoter may drive the transcription of the nuclease and guide nucleic acid sequences but the two inducible promoters may be the same type of inducible promoter. Alternatively, the inducible promoter controlling expression of the nuclease may be different from the inducible promoter controlling transcription of the guide nucleic acid.

In general, a guide nucleic acid (e.g., gRNA) complexes with a compatible nucleic acid-guided nuclease and can then hybridize with a target sequence, thereby directing the nuclease to the target sequence. In certain aspects, the RNA-guided enzyme editing system may use two separate guide nucleic acid molecules that combine to function as a guide nucleic acid, e.g., a CRISPR RNA (crRNA) and trans-activating CRISPR RNA (tracrRNA). In other aspects—and used with the MAD70-series variant nucleases described herein—the guide nucleic acid may be a single guide nucleic acid that includes both the crRNA and tracrRNA sequences. A guide nucleic acid can be DNA or RNA; alternatively, a guide nucleic acid may comprise both DNA and RNA. In some embodiments, a guide nucleic acid may comprise modified or non-naturally occurring nucleotides. In cases where the guide nucleic acid comprises RNA, the gRNA may be encoded by a DNA sequence on a polynucleotide molecule such as a plasmid, linear construct, or the coding sequence may reside within an editing cassette and is under the control of a constitutive promoter, or, in some embodiments, an inducible promoter as described below.

A guide nucleic acid comprises a guide sequence, where the guide sequence is a polynucleotide sequence having sufficient complementarity with a target sequence to hybridize with the target sequence and direct sequence-specific binding of a complexed nucleic acid-guided nuclease to the target sequence. The degree of complementarity between a guide sequence and the corresponding target sequence, when optimally aligned using a suitable alignment algorithm, is about or more than about 50%, 60%, 75%, 80%, 85%, 90%, 95%, 97.5%, 99%, or more. Optimal alignment may be determined with the use of any suitable algorithm for aligning sequences. In some embodiments, a guide sequence is about or more than about 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 75, or more nucleotides in length. In some embodiments, a guide sequence is less than about 75, 50, 45, 40, 35, 30, 25, 20 nucleotides in length. Preferably the guide sequence is 10-30 or 15-20 nucleotides long, or 15, 16, 17, 18, 19, or 20 nucleotides in length.

In the present methods and compositions, the guide nucleic acid typically is provided as a sequence to be expressed from a plasmid or vector and comprises both the guide sequence and the scaffold sequence as a single transcript under the control of a promoter, and in some embodiments, an inducible promoter. The guide nucleic acid can be engineered to target a desired target sequence by altering the guide sequence so that the guide sequence is complementary to a desired target sequence, thereby allowing hybridization between the guide sequence and the target sequence. In general, to generate an edit in the target sequence, the gRNA/nuclease complex binds to a target sequence as determined by the guide RNA, and the nuclease recognizes a protospacer adjacent motif (PAM) sequence adjacent to the target sequence. The target sequence can be any polynucleotide endogenous or exogenous to a prokaryotic or eukaryotic cell, or in vitro. For example, the target sequence can be a polynucleotide residing in the nucleus of a eukaryotic cell. A target sequence can be a sequence encoding a gene product (e.g., a protein) or a non-coding sequence (e.g., a regulatory polynucleotide, an intron, a PAM, or “junk” DNA).

The guide nucleic acid may be part of an editing cassette that encodes the donor nucleic acid, such as described in U.S. U.S. Pat. No. 10,240,167, issued 26 Mar. 2019; U.S. Pat. No. 10,266,849, issued 23 Apr. 2019; U.S. Pat. No. 9,982,278, issued 22 Jun. 2018; U.S. Pat. No. 10,351,877, issued 15 Jul. 2019; and U.S. Pat. No. 10,362,422, issued 30 Jul. 2019; and U.S. Ser. No. 16/275,439, filed 14 Feb. 2019; Ser. No. 16/275,465, filed 14 Feb. 2019; Ser. No. 16/550,092, filed 23 Aug. 2019; and Ser. No. 16/552,517, filed 26 Aug. 2019. Alternatively, the guide nucleic acid may not be part of the editing cassette and instead may be encoded on the engine or editing vector backbone. For example, a sequence coding for a guide nucleic acid can be assembled or inserted into a vector backbone first, followed by insertion of the donor nucleic acid in, e.g., the editing cassette. In other cases, the donor nucleic acid in, e.g., an editing cassette can be inserted or assembled into a vector backbone first, followed by insertion of the sequence coding for the guide nucleic acid. In yet other cases, the sequence encoding the guide nucleic acid and the donor nucleic acid (inserted, for example, in an editing cassette) are simultaneously but separately inserted or assembled into a vector. In yet other embodiments, the sequence encoding the guide nucleic acid and the sequence encoding the donor nucleic acid are both included in the editing cassette.

The target sequence is associated with a PAM, which is a short nucleotide sequence recognized by the gRNA/nuclease complex. The precise PAM sequence and length requirements for different nucleic acid-guided nucleases vary; however, PAMs typically are 2-7 base-pair sequences adjacent or in proximity to the target sequence and, depending on the nuclease, can be 5′ or 3′ to the target sequence. Engineering of the PAM-interacting domain of a nucleic acid-guided nuclease may allow for alteration of PAM specificity, improve fidelity, or decrease fidelity. In certain embodiments, the genome editing of a target sequence both introduces a desired DNA change to a target sequence, e.g., the genomic DNA of a cell, and removes, mutates, or renders inactive a proto-spacer mutation (PAM) region in the target sequence. Rendering the PAM at the target sequence inactive precludes additional editing of the cell genome at that target sequence, e.g., upon subsequent exposure to a nucleic acid-guided nuclease complexed with a synthetic guide nucleic acid in later rounds of editing. Thus, cells having the desired target sequence edit and an altered PAM can be selected using a nucleic acid-guided nuclease complexed with a synthetic guide nucleic acid complementary to the target sequence. Cells that did not undergo the first editing event will be cut rendering a double-stranded DNA break, and thus will not continue to be viable. The cells containing the desired target sequence edit and PAM alteration will not be cut, as these edited cells no longer contain the necessary PAM site and will continue to grow and propagate.

The range of target sequences that nucleic acid-guided nucleases can recognize is constrained by the need for a specific PAM to be located near the desired target sequence. As a result, it often can be difficult to target edits with the precision that is necessary for genome editing. It has been found that nucleases can recognize some PAMs very well (e.g., canonical PAMs), and other PAMs less well or poorly (e.g., non-canonical PAMs). Because certain of the engineered MAD70-series nucleases disclosed herein recognize different PAMs, the engineered MAD70-series nucleases increase the number of target sequences that can be targeted for editing; that is, engineered MAD70-series nucleases decrease the regions of “PAM deserts” in the genome. Thus, the engineered MAD70-series nucleases expand the scope of target sequences that may be edited by increasing the number (variety) of PAM sequences recognized. Moreover, cocktails of engineered MAD70-series nucleases may be delivered to cells such that target sequences adjacent to several different PAMs may be edited in a single editing run.

Another component of the nucleic acid-guided nuclease system is the donor nucleic acid. In some embodiments, the donor nucleic acid is on the same polynucleotide (e.g., editing vector or editing cassette) as the guide nucleic acid and may be (but not necessarily) under the control of the same promoter as the guide nucleic acid (e.g., a single promoter driving the transcription of both the guide nucleic acid and the donor nucleic acid). The donor nucleic acid is designed to serve as a template for homologous recombination with a target sequence nicked or cleaved by the nucleic acid-guided nuclease as a part of the gRNA/nuclease complex. A donor nucleic acid polynucleotide may be of any suitable length, such as about or more than about 20, 25, 50, 75, 100, 150, 200, 500, or 1000 nucleotides in length. In certain preferred aspects, the donor nucleic acid can be provided as an oligonucleotide of between 20-300 nucleotides, more preferably between 50-250 nucleotides. The donor nucleic acid comprises a region that is complementary to a portion of the target sequence (e.g., a homology arm). When optimally aligned, the donor nucleic acid overlaps with (is complementary to) the target sequence by, e.g., about 20, 25, 30, 35, 40, 50, 60, 70, 80, 90 or more nucleotides. In many embodiments, the donor nucleic acid comprises two homology arms (regions complementary to the target sequence) flanking the mutation or difference between the donor nucleic acid and the target template. The donor nucleic acid comprises at least one mutation or alteration compared to the target sequence, such as an insertion, deletion, modification, or any combination thereof compared to the target sequence.

As mentioned previously, often the donor nucleic acid is provided as an editing cassette, which is inserted into a vector backbone where the vector backbone may comprise a promoter driving transcription of the gRNA and the coding sequence of the gRNA, or the vector backbone may comprise a promoter driving the transcription of the gRNA but not the gRNA itself. Moreover, there may be more than one, e.g., two, three, four, or more guide nucleic acid/donor nucleic acid cassettes inserted into an engine vector, where each guide nucleic acid is under the control of separate different promoters, separate like promoters, or where all guide nucleic acid/donor nucleic acid pairs are under the control of a single promoter. In some embodiments—such as embodiments where cell selection is employed—the promoter driving transcription of the gRNA and the donor nucleic acid (or driving more than one gRNA/donor nucleic acid pair) is an inducible promoter. Inducible editing is advantageous in that singulated cells can be grown for several to many cell doublings before editing is initiated, which increases the likelihood that cells with edits will survive, as the double-strand cuts caused by active editing are largely toxic to the cells. This toxicity results both in cell death in the edited colonies, as well as a lag in growth for the edited cells that do survive but must repair and recover following editing. However, once the edited cells have a chance to recover, the size of the colonies of the edited cells will eventually catch up to the size of the colonies of unedited cells. See, e.g., U.S. Ser. No. 16/399,988, filed 30 Apr. 2019; Ser. No. 16/454,865 filed 26 Jun. 2019; and Ser. No. 16/540,606, filed 14 Aug. 2019. Further, a guide nucleic acid may be efficacious directing the edit of more than one donor nucleic acid in an editing cassette; e.g., if the desired edits are close to one another in a target sequence.

In addition to the donor nucleic acid, an editing cassette may comprise one or more primer sites. The primer sites can be used to amplify the editing cassette by using oligonucleotide primers; for example, if the primer sites flank one or more of the other components of the editing cassette.

Also, as described above, the donor nucleic acid may comprise—in addition to the at least one mutation relative to a target sequence—one or more PAM sequence alterations that mutate, delete or render inactive the PAM site in the target sequence. The PAM sequence alteration in the target sequence renders the PAM site “immune” to the nucleic acid-guided nuclease and protects the target sequence from further editing in subsequent rounds of editing if the same nuclease is used.

In addition, the editing cassette may comprise a barcode. A barcode is a unique DNA sequence that corresponds to the donor DNA sequence such that the barcode can identify the edit made to the corresponding target sequence. The barcode typically comprises four or more nucleotides. In some embodiments, the editing cassettes comprise a collection of donor nucleic acids representing, e.g., gene-wide or genome-wide libraries of donor nucleic acids. The library of editing cassettes is cloned into vector backbones where, e.g., each different donor nucleic acid is associated with a different barcode.

Additionally, in some embodiments, an expression vector or cassette encoding components of the nucleic acid-guided nuclease system further encodes an engineered MAD70-series nuclease comprising one or more nuclear localization sequences (NLSs), such as about or more than about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more NLSs. In some embodiments, the engineered nuclease comprises NLSs at or near the amino-terminus, NLSs at or near the carboxy-terminus, or a combination.

The engine and editing vectors comprise control sequences operably linked to the component sequences to be transcribed. As stated above, the promoters driving transcription of one or more components of the engineered MAD70-series nuclease editing system may be inducible, and an inducible system is likely employed if selection is to be performed. A number of gene regulation control systems have been developed for the controlled expression of genes in plant, microbe, and animal cells, including mammalian cells, including the pL promoter (induced by heat inactivation of the CI857 repressor), the pBAD promoter (induced by the addition of arabinose to the cell growth medium), and the rhamnose inducible promoter (induced by the addition of rhamnose to the cell growth medium). Other systems include the tetracycline-controlled transcriptional activation system (Tet-On/Tet-Off, Clontech, Inc. (Palo Alto, Calif.); Bujard and Gossen, PNAS, 89(12):5547-5551 (1992)), the Lac Switch Inducible system (Wyborski et al., Environ Mol Mutagen, 28(4):447-58 (1996); DuCoeur et al., Strategies 5(3):70-72 (1992); U.S. Pat. No. 4,833,080), the ecdysone-inducible gene expression system (No et al., PNAS, 93(8):3346-3351 (1996)), the cumate gene-switch system (Mullick et al., BMC Biotechnology, 6:43 (2006)), and the tamoxifen-inducible gene expression (Zhang et al., Nucleic Acids Research, 24:543-548 (1996)) as well as others.

Typically, performing genome editing in live cells entails transforming cells with the components necessary to perform nucleic acid-guided nuclease editing. For example, the cells may be transformed simultaneously with separate engine and editing vectors; the cells may already be expressing the engineered MAD70-series nuclease (e.g., the cells may have already been transformed with an engine vector or the coding sequence for the engineered MAD70-series nuclease may be stably integrated into the cellular genome) such that only the editing vector needs to be transformed into the cells; or the cells may be transformed with a single vector comprising all components required to perform nucleic acid-guided nuclease genome editing.

A variety of delivery systems can be used to introduce (e.g., transform or transfect) nucleic acid-guided nuclease editing system components into a host cell. These delivery systems include the use of yeast systems, lipofection systems, microinjection systems, biolistic systems, virosomes, liposomes, immunoliposomes, polycations, lipid:nucleic acid conjugates, virions, artificial virions, viral vectors, electroporation, cell permeable peptides, nanoparticles, nanowires, exosomes. Alternatively, molecular trojan horse liposomes may be used to deliver nucleic acid-guided nuclease components across the blood brain barrier. Of particular interest is the use of electroporation, particularly flow-through electroporation (either as a stand-alone instrument or as a module in an automated multi-module system) as described in, e.g., U.S. U.S. Pat. No. 10,435,717, issued 8 Oct. 2019; and U.S. Pat. No. 10,443,074, issued 15 Oct. 2019; U.S. Ser. No. 16/550,790, filed 26 Aug. 2019; Ser. No. 10/323,258, issued 18 Jun. 2019; and Ser. No. 10/415,058, issued 17 Sep. 2019.

After the cells are transformed with the components necessary to perform nucleic acid-guided nuclease editing, the cells are cultured under conditions that promote editing. For example, if constitutive promoters are used to drive transcription of the engineered MAD70-series nucleases and/or gRNA, the transformed cells need only be cultured in a typical culture medium under typical conditions (e.g., temperature, CO₂ atmosphere, etc.) Alternatively, if editing is inducible—by, e.g., activating inducible promoters that control transcription of one or more of the components needed for nucleic acid-guided nuclease editing, such as, e.g., transcription of the gRNA, donor DNA, nuclease, or, in the case of bacteria, a recombineering system—the cells are subjected to inducing conditions. The MAD70 nucleases described herein may be used in automated systems, such as those described in U.S. Pat. No. 10,253,316, issued 9 Apr. 2019; U.S. Pat. No. 10,329,559, issued 25 Jun. 2019; U.S. Pat. No. 10,323,242, issued 18 Jun. 2019; and U.S. Pat. No. 10,421,959, issued 24 Sep. 2019; and U.S. patent Ser. No. 16/412,195, filed 14 May 2019; Ser. No. 16/423,289, filed 28 May 2019; and Ser. No. 16/571,091, filed 14 Sep. 2019.

EXAMPLES

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the present invention, and are not intended to limit the scope of what the inventors regard as their invention, nor are they intended to represent or imply that the experiments below are all of or the only experiments performed. It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific aspects without departing from the spirit or scope of the invention as broadly described. The present aspects are, therefore, to be considered in all respects as illustrative and not restrictive.

Example 1: Exemplary Workflow Overview

FIG. 3 shows an exemplary workflow 300 for creating and screening engineered MAD70-series enzymes. In a first step 301, a wild type MAD7 DNA sequence was prepared and cloned to make a template vector for creation of MAD70-series variants. In another step 303, computer homology modeling of MAD7 (represented by an amino acid sequence having the sequence SEQ ID No. 1) was performed to identify putative regions of interest for rationally-designing MAD70 variants with varied PAM preferences, optimized activity in specific organisms, and altered fidelity as compared to MAD7. These regions include regions of the nuclease proximal to key regions where it is predicted that the nuclease interacts with the PAM, target, or gRNA e.g., see Example 2 below. Once putative key regions of interest were identified in silico, cassettes were constructed and cloned into the vector template, then transformed into cells 305, thereby generating a library of engineered MAD70-series variants. The cells transformed with the engineered MAD70-series variants were arrayed in 96-well plates 307 for storage. At step 309, an aliquot of the cells from each well was taken, and the MAD70-series sequences were amplified from each aliquot. At another step 311, a plasmid expressing a gRNA was constructed, and then combined with the amplified MAD70-series nucleases to perform in vitro transcription and translation to make active ribonuclease protein complexes 313. A synthetic target library was constructed 315, in which to test target depletion 317 for each of that MAD70-series variants. After target depletion, amplicons were produced for analysis using next-gen sequencing 319, and sequencing data analysis was performed 321 to determine target depletion.

Example 2: Homology Modeling and Positions for Mutation Testing

An in silico homology model of a MAD7 enzyme having the amino acid sequence as represented by SEQ ID No. 1 was made using PDB:5B43 structure as a template using SWISS-MODEL (https://swissmodel.expasy.org/). Mutation sets were generated based on residue proximity to putative key regions of where the nuclease is predicted to interact with the PAM site, target, or gRNA, as well as targeting charged amino acids. The following amino acid residues were targeted for mutation (the residues are in relation to the MAD7 amino acid sequence in SEQ ID No. 1): 19, 22, 55, 84, 95, 124, 125, 159, 160, 161, 162, 165, 169, 171, 187, 269, 278, 281, 283, 284, 346, 466, 505, 511, 517, 528, 529, 530, 531, 532, 533, 534, 535, 536, 539, 582, 584, 586, 587, 588, 589, 590, 591, 593, 594, 595, 596, 597, 598, 599, 600, 601, 620, 623, 650, 707, 712, 720, 739, 741, 742, 743, 749, 761, 768, 785, 786, 822, 830, 833, 842, 853, 878, 881, 912, 920, 924, 925, 932, 934, 937, 946, 969, 970, 974, 982, 990, 997, 1019, 1021, 1052, 1054, 1109, 1111, 1113, 1173.

Example 3: Vector Cloning, MAD70-Series Variant Library Construction and PCR

The MAD7 coding sequence was cloned into a pUC57 vector with T7-promoter sequence attached to the 5′-end of the coding sequence and a T7-terminator sequence attached to the 3′-end of the coding sequence. Next, using a pUC57-MAD7 wildtype vector as a template, a saturated mutation library for the 96 positions predicted by the modeling described in Example 2 was made substituting the original codon with NNK (IUPAC code for DNA: N=A, T, G, C; K=G, T) randomized codons. The engineered MAD70-series variants were delivered as a pool of mutant plasmids. 100 ng of a plasmid mixture was transformed into five E.cloni® SUPREME electrocompetent solo cells (Lucigen). After the cells were recovered in 5 mL of recovery medium at 37° C. for 1 hr in a shaking incubator, 1 mL of 50% glycerol was added and the cells were stored at −80° C. as 100 μL aliquots.

The stored cells were diluted in phosphate buffered saline and spread on LB agar plates with 100 μg/mL of carbenicillin. The cells were then grown overnight at 37° C. in an incubator. Colonies were picked and inoculated into 1 mL of LB medium (100 μg/mL of carbenicillin) in 96-well culture blocks. Cultures were grown overnight in a shaking incubator at 37° C. Next, 1 μL of the cells were diluted into 500 μL of PCR grade water, and 25 μl aliquots of diluted cultures were boiled for 5 min at 95° C. using a thermal cycler. The boiled cells were used to PCR amplify the different engineered MAD70-series variant coding sequences. The rest of the cultures were stored at −80° C. with added glycerol at 10% v/v concentration.

First, Q5 Hot Start 2× master mix reagent (NEB) was used to amplify the engineered MAD70-series variant sequences using the boiled cells as a source of MAD70-series variant templates. The forward primer 5′-TTGGGTAACGCCAGGGTTTT (SEQ ID No. 16) and reverse primer 5′-TGTGTGGAATTGTGAGCGGA (SEQ ID No. 17) amplified the sequences flanking the engineered MAD70-series variant in the pUC57 vector including the T7-promoter and T7-terminator components attached to the MAD7 variant sequence at the 5′- and 3′-end of the engineered MAD70-series variants, respectively. 1 μM primers were used in a 10 μL PCR reaction using 3.3 μL boiled cell samples as templates in 96 well PCR plates. The PCR conditions shown in Table 1 were used:

TABLE 1 PCR conditions STEP TEMPERATURE TIME DENATURATION 98° C. 30 SEC 30 CYCLES 98° C. 10 SEC 66° C. 30 SEC 72° C. 2.5 MIN FINAL 72° C. 2 MIN EXTENSION HOLD 12° C.

Example 4: gRNA Expression Gene Construction in Plasmids and Synthetic Target Library Construction

Two plasmids were made to produce two different guide RNAs for the in vitro depletion assay. A MAD7 gRNA scaffold sequence (5′-GGAATTTCTACTCTTGTAGAT (SEQ ID No. 18)) was placed under the control of the T7 promoter followed by a guide sequence for synthetic Target 3 or Target 7. The sequences of these constructs are shown in FIG. 4.

Two different synthetic target sequences were used to design a synthetic plasmid target library, where the target oligo pools were ordered from Twist Bioscience (Carlsbad, Calif.) using the following designs: Target sequence: Target3: 5′-CCAGTCAGTAATGTTACTGG (SEQ ID No. 19), and Target7: 5′-AGCAGGACACTCCTGCCCCA (SEQ ID No. 20).

TABLE 2 Target Library Design: NUMBER OF PAMs TARGET FOR VARIANT/ LIBRARY PAM 5′ 3′ UMI ANALYSIS DESIGN PAM PANEL TNNN N 64 1 SPECIFICITY TTTV N 3 12 PANEL

The PAM panel library was designed by adding TNNN randomized sequences as the 5′-end PAM for each target, then by adding a single bp N at the end of the target to be used as the unique molecular identifier in the sequencing analysis. The specificity panel was designed by introducing 2 bp tandem mismatches in the following positions in each target: 1st, 3rd, 7th, 8th, 9th, 11th, 13th, 14th, 15th, 17th, 18th, and 19th bp. Each target with 2 bp mismatches was used to add 5′-end TTTV PAM (IUPAC nomenclature: V=A,G, or C) and 3′-end 1 bp N as the UMI (unique molecule identifier) for sequencing analysis. The target library was cloned into a pUC19 backbone and prepared using the Midi-plus™ plasmid preparation kit (Qiagen). The target library pool was prepared at 10 ng/μL final concentration.

Example 5: In Vitro Transcription and Translation for Production of MAD70-Series Nucleases and gRNAs in a Single Well

A PURExpress® In Vitro Protein Synthesis Kit (NEB) was used to produce engineered MAD70-series variant proteins from the PCR-amplified MAD70-series variant library, and also to produce gRNAs for synthetic target Library of Target3 and Target7. In each well in a 96-well plate, the reagents in Table 3 were mixed to start the production of MAD7 variants and gRNA:

TABLE 3 Reagents REAGENTS VOLUME (μl) 1 SolA (NEB kit) 3.3 2 SolB (NEB kit) 2.5 3 gRNA mix (4 ng/μl stock) 0.8 4 Murine RNase inhibitor (NEB) 0.2 5 Water 0.5 6 PCR amplified T7 1.0 MAD70-series variants

A master mix with all reagents was mixed on ice with the exception of the PCR-amplified T7-MAD70-series variants to cover enough 96-well plates for the assay. After 7.3 μL of the master mix was distributed in each well in 96 well plates, 1 μL of the PCR amplified MAD70-series variants under the control of T7 promoter was added. The 96-well plates were sealed and incubated for 4 hrs at 37° C. in a thermal cycler. The plates were kept at room temperature until the target pool was added to perform the target depletion reaction.

Example 6: Performing Target Depletion, PCR and NGS

After 4 hours incubation to allow production of the engineered MAD70-series variants and gRNAs, 4 μL of the target library pool (10 ng/μL) was added to the in vitro transcription/translation reaction mixture. After the target library was added, reaction mixtures were incubated overnight at 37° C. The target depletion reaction mixtures were diluted into PCR-grade water that contains RNAse A and then boiled for 5 min at 95° C. The mixtures were then amplified and sequenced. The PCR conditions in Table 4 below were used:

TABLE 4 PCR Conditions STEP TEMPERATURE TIME DENATURATION 98° C. 30 SEC 6 CYCLES 98° C. 10 SEC 61° C. 30 SEC 72° C. 10 SEC 22 CYCLES 98° C. 10 SEC 72° C. 10 SEC FINAL EXTENSION 72° C. 2 MINUTES HOLD 12° C.

Example 7: Data Analysis

Table 5 is a table of amino acid substitutions made to the MAD7 nuclease amino acid sequence (SEQ ID No. 1) that result in MAD70-series variant nucleases with different PAM recognition sites as compared to the native MAD7 nuclease.

TABLE 5 MAD70-series Variants-Altered PAM Preference WT Mutation New PAMs, cut Residue Detected detected SEQ ID No. K535L L TGTN, TTCN SEQ ID No. 2 K535S S TGTN, TTCN SEQ ID No. 11 K535C C TGTN, TTCN SEQ ID No. 12 K535R R TGTN, TTCN SEQ ID No. 13 K535N N TGTN, TTCN SEQ ID No. 14 K535G G TCTN as primary SEQ ID No. 3

FIG. 1A is a heatmap for the MAD70-series variant nucleases with different PAM recognition sites. The K535R mutation disrupts the ability of the enzyme to recognize TCTN PAMs and enhances the ability of the enzyme to recognize PAMs containing a purine at the second position (TATN/TGTN). The K594 mutation ablates the recognition of the preferred TTTN PAMs while enhancing TCGN recognition.

Table 6 is a table of amino acid substitutions made to the MAD7 nuclease amino acid sequence (SEQ ID No. 1) resulting in MAD70-series variant nucleases with varied targeting fidelity as compared to the MAD7 reference nuclease.

TABLE 6 MAD70-series Variants-Varied Target Fidelity Mutation Pos_9 score for HF- WT Residue Detected MAD7 (wt > 0.3) SEQ ID No. R920G G 0.0 SEQ ID No. 4 R924I I 0.04 SEQ ID No. 5 K511L L 0.03 SEQ ID No. 6 H283T T 0.01 SEQ ID No. 7 R187K K 0.0 SEQ ID No. 8 N589G G 0.0 SEQ ID No. 9 K281A A 0.04 SEQ ID No. 10 K281V V 0.01 SEQ ID No. 15

FIG. 1B is the heatmap for the MAD70-series variant nucleases with varied fidelity as compared with wild-type MAD7 (SEQ ID No. 1). The bottom figure shows the PAM depletion panel for the same enzyme from the above figure. R187K and N589G showed better pos9 specificity but note from the bottom figure these MAD70-series nucleases showed reduced activity across all PAMs. As can be seen many of these mutations eliminate activity of the enzyme for targets that contain programmed 2 bp mismatches at the +9, +14, +15, and +17 positions relative to the PAM sequence indicating an improved targeting fidelity.

FIG. 2A is a PAM depletion vs specificity plot of the native MAD7 sequence (SEQ ID No. 1) sampled across multiple plates in a HT-screen. The PAM specificity is represented as the sum of the depletion scores observed for all PAMs tested (D_(PAM)) as calculated by Eqn 1: PAM _(score) =ΣD _(PAM)  eqn.1: The relative nuclease specificity is calculated as the pos9_score as shown in eqn 2.

$\begin{matrix} {{pos}_{9_{score}} = \frac{D_{9}}{D_{wt}}} & {{eqn}.\mspace{14mu} 2} \end{matrix}$ Where D₉ is the sum of the depletion scores for DNA target sequences containing a 2 bp mismatch at the PAM +9 position and D_(wt) is the sum of the depletion scores for DNA targets with perfect complementarity to the gRNAs used in this assay. This scoring methodology was chosen empirically based on the sensitivity of the targeting specificity to mutations in this register of the RNA-DNA interaction. Each point corresponds to an independent measurement from control digestion experiments run with the MAD7 nuclease (SEQ ID NO. 1). FIG. 2B is the plot for the screened 1108 single amino acid variants tested. Points in the lower two quadrants represent loss of function mutations which occurred in 433/1020 (43%) of the screened space. Data points in the upper left portion of the graph (>10 sum of Pam_depletion, <0.3 pos_9_depletion/wt_depletion) represent variants that with high activity as judged by their summed PAM activity score and high altered RNA-guided enzyme fidelity relative to the wild-type MAD7 enzyme sequence (FIG. 2A).

Example 8: Combinatorial Mutation Library Construction, Screening and Data Analysis

Based on the results observed in Example 7, an additional mutant library was designed and screened for changes in PAM preference. The library was composed of mutations at both positions K535 and K594 (the residues are in relation to the MAD7 amino acid sequence in SEQ ID No. 1) substituting the original codon with NNK (IUPAC code for DNA: N=A, T, G, C; K=G, T) randomized codons. The library was constructed using a Q5 Site Directed Mutagenesis Kit (NEB) using manufacturers protocols with mutagenic forward 5′-TTCTNNKAACGCTATCATACTGATGC (SEQ ID No. 25) and reverse 5′TACTCMNNGGACTTTGACCAACCGTC (SEQ ID No. 26) primers. The PCR reaction mix was transformed into 5-alpha chemically competent cells (NEB) and plated on LB agar plates with 100 μg/mL of carbenicillin. Colonies were picked and inoculated into 1 mL of LB medium (100 μg/mL of carbenicillin) in 96-well culture blocks and grown overnight in a shaking incubator at 37° C. Sample processing and screening was performed as described in examples 3, 4, 5 and 6.

FIG. 5 is a heatmap for a MAD70-series nuclease with novel PAM recognition sites identified from this library screening (SEQ ID No. 67). This mutant contains the combination of mutations K535R and N539S (SEQ ID No. 67) and results in more robust activity on PAMs with an A nucleotide at the second position of the NNNN PAM space, in particular TAAN, compared to the K535R mutation alone.

Example 9: Revised Target Library

A revised PAM panel library was designed by adding NNNN randomized sequences as the 5′-end PAM for each target, in order to evaluate activity on all 256 PAM sequences in the NNNN PAM space. Oligo pools were ordered from Twist Bioscience (Carlsbad, Calif.) using the following designs: Target3: 5′-CCAGTCAGTAATGTTACTGG (SEQ ID No. 27), and Target7: 5′-AGCAGGACACTCCTGCCCCA (SEQ ID No. 28). The target library was cloned into a pUC19 backbone and prepared using the Midi-plus™ plasmid preparation kit (Qiagen). The target library pool was prepared at 10 ng/μL final concentration.

TABLE 7 Revised Library Number of PAMs for Target Library PAM 5′ 3′ UMI analysis Variant/Design PAM panel NNNN none 256 1 (2 targets)

Example 10: Mutagenic Library Construction, Screening and Data Analysis Using K535R/N539S Backbone

In order to further alter the PAM preference, a library of single amino acid mutations was generated using the K535R/N539S mutant (SEQ ID No. 67) described in Example 8. Mutation sets were generated based on residue proximity to putative key regions of where the nuclease is predicted to interact with the PAM site, target, or gRNA, as well as targeting charged amino acids. The following amino acid residues were targeted for mutation (the residues are in relation to the MAD7 amino acid sequence in SEQ ID No. 1): 529, 530, 531, 532, 534, 536, 537, 538, 540, 541, 582, 583, 584, 585, 586, 587, 588, 589, 590, 591, 592, 593, 594, 595, 599, 601, 650, 739, 740, 741, 742, 743. At each position, the original codon was substituted with NNK (IUPAC code for DNA: N=A, T, G, C; K=G, T) randomized codons. This library was screened for altered PAM preference as described in examples 3, 4, 5 and 6, using the target oligonucleotide library described in Example 9.

FIG. 6 represents activity heatmaps for wild-type MAD7 (SEQ ID No. 1) (FIG. 6A), the K535R/N539S mutant (SEQ ID No. 67) (FIG. 6B) used as the parent for this library, along with an additional MAD70-series nuclease with novel PAM recognition sites identified from this library (SEQ ID No. 68) (FIG. 6C). Data analysis was performed as described in Example 7, with heatmaps now representing activity on all 64 combinations of nucleotides in the NNNN PAM space. The new MAD70-eries nuclease mutant (SEQ ID No. 68) contains the combination of mutations K535R/N539S/K594L/E730Q in relation to the wild-type MAD7 amino acid sequence in SEQ ID No. 1. It has novel activity on PAMs with a C nucleotide at the third position of the NNNN PAM space.

Example 11: Activity of MAD70-series PAM mutants in Escherichia coli cells

In order to confirm activity of the MAD70-series mutants for genome editing systems in cells, activity was confirmed using a phenotypic editing assay in E. coli. MAD70-series mutants were cloned into a EE0026 vector backbone. MAD70-series variants were amplified using reverse (5′ GATGATTTCTCTAGAGGTACTTAGAGATAGCGCTTATTCTGGATAAAGTC) (SEQ ID No. 29) and forward (5′ CGATTCCGGAAAGGAGATATCTCATGAACAACGGCACAAATAATTTTCAG AA) (SEQ ID No. 30) primers and cloned into the linearized EE0026 Engine vector using the NEBuilder HF DNA assembly kit.

Editing cassettes were designed to introduce stop codons to disrupt the synthesis of full-length LacZ in E. coli as a result of editing. Each cassette was composed of a 20 base pair spacer to precisely target a region of lacZ gene in the E. coli genome adjacent to the indicated PAM sequence in the genome, and a 200 bp repair template for homologous recombination. DNA sequences and corresponding PAM targets for each cassette are provided in Table 8. Each cassette is cloned into the common cassette vector backbone p346BB (SEQ ID No. 87) using the NEBuilder HF DNA assembly kit. E. coli K-12 str MG1655 grown to mid-log phase in LB was made electrocompetent by washing three times with ice cold 10% glycerol. Engine vectors were transformed by electroporation, recovered in SOC for 1 hr at 30° C., then grown overnight on LB agar with Chloramphenicol (25 ug/mL) medium at 30° C. Overnight grown cells with MAD70-series variant engine vectors were grown to mid log phase in LB Chloramphenicol (25 ug/mL) and made competent with LB broth containing 10% (wt/vol) polyethylene glycol, 5% (vol/vol) dimethyl sulfoxide, and 50 mM Mg2+ at pH 6.5.

TABLE 8 Sequences of Editing cassettes and corresponding PAM targets Cassette  Target SEQ ID name Insert sequence gene PAM No. lacZ_127_ GTGTGTGATACGAAACGAAGCATTGGAGGCATTG lacZ TTTC 31 TTTC_stop GAATTTCTACTCTTGTAGATACCCTGCCATAAAGA AACTGTCCATGTTGCCACTCGCTTTAATGATGATT TCAGCCGCGCTGTACTGGAGGCTGAAGTTCAGAT GTGCGGCGAGTTGCGTGACTACCTACGGGTAACA TAATGATTATGGTAATGAGAGACCCAGGTCGCCA GCGGCACCGCGCCTTTCGGCGGTGAAATTATCGA TGAGCGTGGTGGTTATGCCGATCGCGTCACACTA ATCCCAGAAAAGACCCGTCCG lacZ_245_ GTGTGTGATACGAAACGAAGCATTGGAGGCATTG lacZ TTTC 32 TTTC_stop GAATTTCTACTCTTGTAGATCATGTTGCCACTCGC TTTAATCACCCTGCCATAAAGAAACTGTTACCCGT AGGTAGTCACGCAACTCGCCGCACATCTGAACTT CAGCCTCCAGTACAGCGCGGCTGAAATCATCATTT CATTAAGTGGCTCATTAGAGATAGCTGATTTGTGT AGTCGGTTTATGCAGCAACGAGACGTCACGGAAA ATGCCGCTCATCCGCCACATATCCTGATCTTCATC CCAGAAAAGACCCGTCCG lacZ_256_ GTGTGTGATACGAAACGAAGCATTGGAGGCATTG lacZ TTTG 33 TTTG_stop GAATTTCTACTCTTGTAGATTGTAGTCGGTTTATG CAGCAACCGCCTCGCGGTGATGGTGCTGCGCTGG AGTGACGGCAGTTATCTGGAAGATCAGGATATGT GGCGGATGAGCGGCATTTTCCGTGACGTCTCGTTG TAATGAAAACCGTAATGACAGATTAGCGATTTCC ATGTTGCCACTCGCTTTAATGATGATTTCAGCCGC GCTGTACTGGAGGCTGAAGTTCAGATGTGCGGCA TCCCAGAAAAGACCCGTCCG lacZ_419_ GTGTGTGATACGAAACGAAGCATTGGAGGCATTG lacZ TTTG 34 TTTG_stop GAATTTCTACTCTTGTAGATCCGTCTGAATTTGAC CTGAGCTCATCCGCCACATATCCTGATCTTCCAGA TAACTGCCGTCACTCCAGCGCAGCACCATCACCG CGAGGCGGTTTTCTCCGGCGCGTAAAAATGCGCTT CATTAAAATTCTCATTACAGACCACTGTCCTGGCC GTAACCGACCCAGCGCCCGTTGCACCACAGATGA AACGCCGAGTTAACGCCATCAAAAATAATTCGAT CCCAGAAAAGACCCGTCCG lacZ_314_ GTGTGTGATACGAAACGAAGCATTGGAGGCATTG lacZ TATG 35 TATG_stop GAATTTCTACTCTTGTAGATTGGCGGATGAGCGGC ATTTTTCCAGTACAGCGCGGCTGAAATCATCATTA AAGCGAGTGGCAACATGGAAATCGCTGATTTGTG TAGTCGGTTTATGCAGCAACGAGACGTCACGGAA TCATTAGCTCATTCATTACACATTCTGATCTTCCA GATAACTGCCGTCACTCCAGCGCAGCACCATCAC CGCGAGGCGGTTTTCTCCGGCGCGTAAAAATGCA TCCCAGAAAAGACCCGTCCG lacZ_920_ GTGTGTGATACGAAACGAAGCATTGGAGGCATTG lacZ TATG 36 TATG_stop GAATTTCTACTCTTGTAGATACCATGATTACGGAT TCACTCTATTACGCCAGCTGGCGAAAGGGGGATG TGCTGCAAGGCGATTAAGTTGGGTAACGCCAGGG TTTTCCCAGTCACGACGTTGTAAAACGACGGCCA GTCATTACGTAATTCATTACACTCATGTTTCCTGT GTGAAATTGTTATCCGCTCACAATTCCACACAACA TACGAGCCGGAAGCATAAAGTGTAAAGCCTGGGA TCCCAGAAAAGACCCGTCCG lacZ_1712_ GTGTGTGATACGAAACGAAGCATTGGAGGCATTG lacZ AACG 37 AACG_stop GAATTTCTACTCTTGTAGATCCATCAAAAATAATT CGCGTATTACGGTCAATCCGCCGTTTGTTCCCACG GAGAATCCGACGGGTTGTTACTCGCTCACATTTAA TGTTGATGAAAGCTGGCTACAGGAAGGCCAGACG TAATGAATTTTTTAATGAGTCAATTCGGCGTTTCA TCTGTGGTGCAACGGGCGCTGGGTCGGTTACGGC CAGGACAGTCGTTTGCCGTCTGAATTTGACCTATC CCAGAAAAGACCCGTCCG lacZ_466_ GTGTGTGATACGAAACGAAGCATTGGAGGCATTG lacZ AACG 38 AACG_stop GAATTTCTACTCTTGTAGATGGGATACTGACGAAA CGCCTAATGGCTTTCGCTACCTGGAGAGACGCGC CCGCTGATCCTTTGCGAATACGCCCACGCGATGG GTAACAGTCTTGGCGGTTTCGCTAAATACTGGCAG TAATGACGTCAGTAATGACGACTTCAGGGCGGCT TCGTCTGGGACTGGGTGGATCAGTCGCTGATTAA ATATGATGAAAACGGCAACCCGTGGTCGGCTTAC ATCCCAGAAAAGACCCGTCCG 10 ng of editing cassette plasmid was added to 20 uL of chemically competent E. coli strain with an engine vector on ice. After 30 min, 250 uL of SOC was added and the cultures were incubated in a shaking incubator for 1 hr at 30° C. 30 uL of the resulting cultures were inoculated to 350 uL of LB Carbenicillin (100 ug/mL)/Chloramphenicol (25 ug/mL) and grown overnight in a shaking incubator at 30° C. 4 uL of the overnight cultures were inoculated to fresh 320 uL LB/Carbenicillin (100 ug/mL)/Chloramphenicol (25 ug/mL)/Arabinose (1% w/v) medium and incubated for 3 hrs in a shaking incubator at 30° C. Cultures were moved to a 42° C. shaking incubator to induce the production of RNP complex. After 5 hrs of induction at 42° C., cultures were moved back to the 30° C. shaking incubator and grown overnight. Overnight grown edited strains were spotted on a MacConkey Agar Plates (Teknova) and grown overnight at 37° C. without any antibiotics. Cultures with native LacZ can ferment the lactose in the medium, produces acid that lowers the pH that makes the red color in the colony. Cultures with edited disrupted LacZ can't ferment the lactose and the colonies grow colorless. A summary of editing phenotypes observed for MAD70-series PAM mutants is shown in FIG. 7. Darker spots indicate intact lacZ and lighter spots are cells with lacZ that are edited and thus are non-functional, indicating gene editing activity on the PAMs listed at top.

Example 12: Phenotypic Assay to Measure Genome Editing for MAD7-Derived Mutants in Saccharomyces cerevisiae Cells

To assess the genome editing activity of RNA-guided nucleases in S. cerevisiae, a two micron plasmid was constructed for the sequential introduction of DNA containing an editing cassette with SNR52 promoter-driven crRNA and a CYC1 promoter-driven nuclease protein (see FIG. 8). The editing cassette comprises the crRNA to guide the nuclease to cut at a specific DNA sequence, a short linker, and a repair template containing the mutation of interest flanked by regions of homology to the genome. The screening plasmid (FIG. 8) was linearized by the StuI restriction endonuclease, and the editing cassette was introduced downstream of the SNR52p promoter by isothermal assembly. The editing cassettes inserted into the StuI-linearized plasmid for the introduction of a premature stop codon into the can1 gene, organized by the PAM of the corresponding spacer, are shown in Table 9. The nuclease proteins were amplified by polymerase chain reaction with oligonucleotide primers to introduce an SV40 nuclear localization sequence at the N-terminus consisting of the DNA sequence “ATGGCACCCAAGAAGAAGAGGAAGGTGTTA” (SEQ ID No. 39) corresponding to a protein sequence of “MAPKKKRKVL (SEQ ID No. 40).” The resulting amplified DNA fragment (400 ng, purified) was then co-transformed along with a PsiI-linearized screening plasmid (250 ng) that already contained an editing cassette to assemble the complete editing plasmid by in vivo gap repair. Cells containing a repaired plasmid were selected for in yeast peptone-dextrose (YPD) containing 200 mg/L Geneticin for 3 days at 30 degrees C. in a humidified shaking incubator. The resulting saturated culture was diluted 1:80 into synthetic complete yeast media lacking arginine and containing 50 mg/L of canavanine and grown overnight at 30 degrees C. in a humidified shaking incubator. Because knockout of the Can1 protein allows yeast to grow in the presence of the otherwise toxic analog canavanine, the relative OD600 of the overnight cultures is proportional to the rate of genome mutation induced by the transformed nuclease protein. The MAD70-series variants described in Examples 7 and 8 with altered PAM preference were evaluated in the assay system using the editing cassettes shown in Table 9, targeting various PAMs. The results of this analysis are shown in FIG. 9, where the mutant containing mutations K535R, K539S in reference to the wild-type MAD7 sequence shows substantially higher editing activity on TATV PAMs.

TABLE 9 Editing cassettes targeting yeast can1 gene  to introduce loss of function mutations Cassette name PAM Editing Cassette Sequence SEQ ID No. Can1_S30stop TTTA GGCCCCAAATTCTAATTTCTACTGTTGTAGATAC 41 GACGTTGAAGCTTCACAATTTTTACGCCGACAT AGAGGAGAAGCATATGTACAATGAGCCGGTCAC AACCCTCGAGACACGACGTTGAAGCTTAACAAA CACACCACAGACGTGGGTCAATACCATTGAAAG ATGAGAAAAGTAACAATATACGCGCTCCTGCCC Can1_K42stop TTTA GGCCCCAAATTCTAATTTCTACTGTTGTAGATCT 42 TTTCTCATCTTTCAATGGTTTTTGTATCCTCGCCA TTTACTCTCGTCGGGAAAGAGCGCAATGGATAC AATTCCCCACTTTTCTCATCTTACAATGGTATTG ACCCACGTCTGTGGTGTGTTTGTGAAGCTTCAAC GTCGTCAATATACGCGCTCCTGCCC Can1 _N60stop TTTC GGCCCCAAATTCTAATTTCTACTGTTGTAGATCC 43 GACGAGAGTAAATGGCGATTTTTTCAATACCAT TGAAAGATGAGAAAAGTAAAGAATTGTATCCAT TGCGCTCGTTCCCGACGAGAGTATAAGGCGAGG ATACGTTCTCTATGGAGGATGGCATAGGTGATG AAGATGAAGGAGAAGCAATATACGCGCTCCTGC CC Can1_T115stop TTTA GGCCCCAAATTCTAATTTCTACTGTTGTAGATTC 44 CACACCTCTGACCAACGCTTTTTATTGGTATGAT TGCCCTTGGTGGTACTATTGGTACAGGTCTTTTC ATTGGATTATCCACACCTCTGTAAAACGCCGGC CCAGTGGGCGCTCTTATATCATATTTATTTATGG GTTCTTTGGCATCAATATACGCGCTCCTGCCC Can1_Q158stop TTTC GGCCCCAAATTCTAATTTCTACTGTTGTAGATAC 45 AGTTTTCTCACAAAGATTTTTTTTCTGTCACGCA GTCCTTGGGTGAAATGGCTACATTCATCCCTGTT ACATCCTCGTTCACAGTTTTCTCATAAAGATTCC TTTCTCCAGCATTTGGTGCGGCCAATGGTTACAT GTATTGGTTTTCAATATACGCGCTCCTGCCC Can1_I214stop TTTG GGCCCCAAATTCTAATTTCTACTGTTGTAGATGG 46 TAATTATCACAATAATGATTTTTCATTCAATTTT GGACGTACAAAGTTCCACTGGCGGCATGGATTA GTATTTGGAAGGTAATTATCACATAAATGAACT TGTTCCCTGTCAAATATTACGGTGAATTCGAGTT CTGGGTCGCCAATATACGCGCTCCTGCCC Can1_G72stop TCTA GGCCCCAAATTCTAATTTCTACTGTTGTAGATTG 47 GAGGATGGCATAGGTGATTTTTTAATTGTATCCA TTGCGCTCTTTCCCGACGAGAGTAAATGGCGAG GATACGTTCTCCATGGAGGATGGCATATAAGAT GAAGATGAAGGAGAAGTACAGAACGCTGAAGT GAAGAGAGAGCTTAACAATATACGCGCTCCTGC CC Can1_Q80stop  TCTC GGCCCCAAATTCTAATTTCTACTGTTGTAGATTT 48 CACTTCAGCGTTCTGTACTTTTTCCAATAGTACC ACCAAGGGCAATCATACCAATATGTCTTTGCTT AAGCTCCCCCTTCACTTCAGCGTTTTATACTTCT CCTTCATCTTCATCACCTATGCCATCCTCCATAG AGAACGTATCAATATACGCGCTCCTGCCC Can1_E142stop TGTC GGCCCCAAATTCTAATTTCTACTGTTGTAGATAC 49 GCAGTCCTTGGGTGAAATTTTTTCCAGTGGGCGC TCTTATATCATATTTATTTATGGGTTCTTTGGCAT ATTCGGTCACGCAGTCCTTGGGTTAAATGGCTA CATTCATCCCTGTTACATCCTCTTTCACAGTTTTC TCACAAAGATCAATATACGCGCTCCTGCCC Can1_S152stop TGTG GGCCCCAAATTCTAATTTCTACTGTTGTAGATAG 50 AAAACTGTGAAAGAGGATTTTTTAACCAATACA TGTAACCATTGGCCGCACCAAATGCTGGAGAAA GGAATCTCCCTGAGAAAACTGTGAATTAGGATG TAACAGGGATGAATGTAGCCATTTCACCCAAGG ACTGCGTGACAGCAATATACGCGCTCCTGCCC Can1_V20stop TATG GGCCCCAAATTCTAATTTCTACTGTTGTAGATTA 51 CAATGAGCCGGTCACAACTTTTTGGCATAGCAA TGACAAATTCAAAAGAAGACGCCGACATAGAG GAGAAGCACGGGTACAATGAGCCGTAAACAAC CCTCTTTCACGACGTTGAAGCTTCACAAACACA CCACAGACGTGGGTCAACAATATACGCGCTCCT GCCC Can1_N116stop TATC GGCCCCAAATTCTAATTTCTACTGTTGTAGATCA 52 CACCTCTGACCAACGCCGTTTTTGTATGATTGCC CTTGGTGGTACTATTGGTACAGGTCTTTTCATTG GTTTAAGTACACCTCTGACCTAAGCCGGCCCAG TGGGCGCTCTTATATCATATTTATTTATGGGTTC TTTGGCATATTCCAATATACGCGCTCCTGCCC

Example 13: Testing of MAD7 Variant Proteins for Enhanced Genome Editing in S. cerevisiae

To screen libraries of MAD7 enzyme variants with one or more mutations for increased genome editing activity in S. cerevisiae, six different editing cassettes (all targeting the TTTV PAM class) (first six entries in Table 9 (SEQ ID Nos. 41-46)) were inserted into the StuI-linearized two micron screening plasmid (again see FIG. 8) as described in Example 12. MAD7 protein variant coding sequences as described in Example 2 were amplified by polymerase chain reaction with oligonucleotide primers to introduce an SV40 nuclear localization sequence at the N-terminus consisting of the DNA sequence “ATGGCACCCAAGAAGAAGAGGAAGGTGTTA” (SEQ ID No. 39) corresponding to a protein sequence of “MAPKKKRKVL (SEQ ID No. 40).” The resulting amplified DNA fragment (5 uL of crude PCR mixture) was then co-transformed along with a PsiI-linearized screening plasmid (150 ng total, a pool of all 6 editing cassettes) that already contains an editing cassette to assemble the complete editing plasmid by in vivo gap repair. Cells containing a repaired plasmid were selected for in yeast peptone-dextrose (YPD) containing 200 mg/L Geneticin for 3 days at 30° C. in a humidified shaking incubator. The resulting saturated culture was diluted into synthetic complete yeast media lacking arginine and containing 50 mg/L of canavanine and grown overnight at 30° C. in a humidified shaking incubator. Because knockout of the Can1 protein allows yeast to grow in the presence of the otherwise toxic analog canavanine, the relative OD600 of the overnight cultures is proportional to the rate of genome mutation induced by the transformed nuclease protein. The relative genome editing activity levels of each variant are plotted in FIG. 10. Rescreening of the variants in quadruplicate in the original assay confirmed the enhanced genome editing activity of several MAD70-series variants, as shown in FIG. 11. Sequences are provided in SEQ ID Nos. 69 (K95L), 70 (V201I/K278T), 71 (K511D), 72 (N589H), 73 (L597V), 74 (K712V), 75 (E743I), 76 (K786S), 77 (K853R), and 78 (R1113F).

Example 14: Generation of Combinatorial MAD7 Variant Libraries and Screening for Enhanced Editing in S. cerevisiae

Based on the identified single mutations that enhance the genome editing activity of MAD7 in S. cerevisiae, combinatorial libraries were prepared. The N589H MAD70-series variant sequence (SEQ ID No. 72) was used as a backbone and 4 to 5 additional mutations were introduced using oligonucleotide primers and the Quick-Change Lightning Multi-Site Mutagenesis kit (Agilent) according to manufacturer instructions. These variants were screened for genome editing activity in S. cerevisiae as described in Example 12 as depicted in FIG. 12. The variants that showed enhanced activity in the primary screen were rescreened in quadruplicate and the results of the secondary screening are depicted in FIG. 13. Sequences are provided in SEQ ID Nos. 79 (S124T/K511I/N589H/K712V/K853R/H946W), 80 (S124T/K511I/N589H/K786S/H946K/R113F), 81 (K511H/N589H/K853R/K102IL/D118E/DE11833), 82 (K95L/S124T/K511I/N589H), 83 (S124T/K511I/N589H/K7211/K786S/K1021V), 84 (S124T/K511H/N589H/K853R/H946K/K1054Y), 85 (K95T/S124T/N589H/K853R/K1052Q), and 86 (S124T/K511T/N589H/K712L/H946T/K1052Q/K1054N).

Example 15: Activity of MAD70-Series PAM Mutants in Mammalian Cells

Wild-type MAD7 and MAD70-series variants with altered PAM preference were cloned downstream of a CAG promoter for strong expression in mammalian cells. The vector sequence used for expression is provided in SEQ ID No. 89. Guide RNAs (gRNAs) targeting various PAMs were cloned downstream of a U6 promoter in the backbone vector sequence provided in SEQ ID No. 90. Transfections in HEK293T cells were performed using 100 ng of total DNA (gRNA/MAD70-series variant plasmid) and Lipofectamine 3000 transfection reagent. The transfection mix was added to cells that had been cultured in 96 well plates 24 hrs prior to transfection. To measure indels, T7E1 assay was performed. Cells were lysed by the addition of a buffer containing proteinase K and incubation at 56° C. for 30 minutes. Proteinase K was inactivated by heating the reaction to 95° C. for 10 minutes. Following lysis, 10 uL PCR reactions were performed using genomic template from lysed cells and 2× Q5 PCR mastermix (NEB) to amplify amplicons containing the target sites that were edited. Following PCR, the PCR fragments were heated to 95° C. C for 5 minutes and slowly cooled to room temperature. Then, T7 endonuclease I (NEB) was added to the PCR reaction and incubated for 1 hour at 37° C. The reaction was then resolved on 2.5% agarose gel and imaged using GelDoc (BioRad). The band intensities on the gel were quantified to calculate indels introduced by MAD7. The results are shown in FIG. 14. The MAD70-series mutant containing mutations K535R/N539S (SEQ ID No. 67) in reference to the wild-type MAD7 sequence shows substantially higher editing activity on TATC PAM while the K535R/N539S/K594L/E730Q (SEQ ID No. 68) mutant in relation to wild-type MAD7 shows higher editing on ATCC and TTCC PAMs.

TABLE 10 Sequences of spacers and the PAM sequences that were targeted in the PPIB locus Target # PAM Spacer Sequence SEQ ID No. 1 CTTC cctcccctagcaacgcccctt 53 2 CATA ggatttttaccgtcaccaaaa 54 3 AATA tggctctattctctctcccat 55 4 ATCG gctgaactctgcaggtcagtt 56 5 ATCC tcaggttagcttcttgtacct 57 6 AATC agattcagaaccacttctcta 58 7 TATC ctgtagtccaaggagggtata 59 8 TATA gataagcatgttttccaagaa 60 9 AACG cccctttaaagaagctaagtt 61 10 AACC acttctctaaaaatatggctc 62 11 TTTT tcagattcagaaccacttctc 63 12 TTTT tatggctctattctctctccc 64 13 ATTC tctctcccatcctcaggttag 65 14 TTCC tcaggtgtattttgacctacg 66

While this invention is satisfied by embodiments in many different forms, as described in detail in connection with preferred embodiments of the invention, it is understood that the present disclosure is to be considered as exemplary of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated and described herein. Numerous variations may be made by persons skilled in the art without departure from the spirit of the invention. The scope of the invention will be measured by the appended claims and their equivalents. The abstract and the title are not to be construed as limiting the scope of the present invention, as their purpose is to enable the appropriate authorities, as well as the general public, to quickly determine the general nature of the invention. In the claims that follow, unless the term “means” is used, none of the features or elements recited therein should be construed as means-plus-function limitations pursuant to 35 U.S.C. § 112, ¶6. 

We claim:
 1. An engineered nucleic acid-guided nuclease with an altered fidelity relative to the nucleic acid-guided nuclease having the sequence of SEQ ID No. 1, wherein the engineered nucleic acid-guided nuclease has a sequence comprising any of SEQ ID Nos. 4-7.
 2. The engineered nucleic acid-guided nuclease of claim 1 comprising SEQ ID No.
 4. 3. The engineered nucleic acid-guided nuclease of claim 1 comprising SEQ ID No.
 5. 4. The engineered nucleic acid-guided nuclease of claim 1 comprising SEQ ID No.
 6. 5. The engineered nucleic acid-guided nuclease of claim 1 comprising SEQ ID No.
 7. 6. An enzyme cocktail comprising an engineered nucleic acid-guided nuclease of claim
 1. 7. An enzyme cocktail comprising an engineered nucleic acid-guided nuclease of claim 1 and SEQ ID No.
 2. 8. An enzyme cocktail comprising an engineered nucleic acid-guided nuclease of claim 1 and SEQ ID No.
 3. 9. An enzyme cocktail comprising an engineered nucleic acid-guided nuclease of claim 1 and SEQ ID No.
 11. 10. An enzyme cocktail comprising an engineered nucleic acid-guided nuclease of claim 1 and SEQ ID No.
 12. 11. An enzyme cocktail comprising an engineered nucleic acid-guided nuclease of claim 1 and SEQ ID No.
 13. 12. An enzyme cocktail comprising an engineered nucleic acid-guided nuclease of claim 1 and SEQ ID No.
 14. 13. An enzyme cocktail comprising an engineered nucleic acid-guided nuclease of claim 1 and SEQ ID No.
 67. 14. An enzyme cocktail comprising an engineered nucleic acid-guided nuclease of claim 1 and SEQ ID No.
 68. 